There is tremendous interest in the Sodium Fluoride study that was just completed by the NTP. However, an equivocal tumorigenic response occurred in male rats, but no response was observed in female rats or mice. Male rats appear to be more sensitive to the potential carcinogenic effects of NaF than female rats or mice. Since irradiation can be altered to produce, various osteosarcoma rates, this follow-up study would be an obvious means of evaluating the possible promoting activity of NaF. The objective is to determine whether radiation induced osteosarcoma in rats is influenced by exposure to NaF in the drinking water. Male F344 rats are given NaF at 0 and 275 ppm in drinking water daily for 10 months following irradiation. Irradiation (3000 rads) subjects to the right rear limb of rat with 137 Cs source. At the end of the 2-year duration of the study, the surviving animals will be humanely killed, tissues collected, fixed, and then slides made and evaluated histopathologically.